[PATCH v3 10/35] x86/bugs: Restructure gds mitigation

David Kaplan
2025-01-08T20:25:50Z

Restructure gds mitigation to use select/apply functions to create
consistent vulnerability handling.

Define new AUTO mitigation for gds.

Signed-off-by: David Kaplan <david.kaplan@amd.com>
---
arch/x86/kernel/cpu/bugs.c | 24 +++++++++++++++++++-----
1 file changed, 19 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index fedd693b2218..58ac99b74bd3 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -76,6 +76,7 @@ static void __init srbds_apply_mitigation(void);
static void __init l1d_flush_select_mitigation(void);
static void __init srso_select_mitigation(void);
static void __init gds_select_mitigation(void);
+static void __init gds_apply_mitigation(void);

/* The base value of the SPEC_CTRL MSR without task-specific bits set */
u64 x86_spec_ctrl_base;
@@ -220,6 +221,7 @@ void __init cpu_select_mitigations(void)
mmio_apply_mitigation();
rfds_apply_mitigation();
srbds_apply_mitigation();
+ gds_apply_mitigation();
}

/*
@@ -811,6 +813,7 @@ early_param("l1d_flush", l1d_flush_parse_cmdline);

enum gds_mitigations {
GDS_MITIGATION_OFF,
+ GDS_MITIGATION_AUTO,
GDS_MITIGATION_UCODE_NEEDED,
GDS_MITIGATION_FORCE,
GDS_MITIGATION_FULL,
@@ -819,7 +822,7 @@ enum gds_mitigations {
};

static enum gds_mitigations gds_mitigation __ro_after_init =
- IS_ENABLED(CONFIG_MITIGATION_GDS) ? GDS_MITIGATION_FULL : GDS_MITIGATION_OFF;
+ IS_ENABLED(CONFIG_MITIGATION_GDS) ? GDS_MITIGATION_AUTO : GDS_MITIGATION_OFF;

static const char * const gds_strings[] = {
[GDS_MITIGATION_OFF] = "Vulnerable",
@@ -860,6 +863,7 @@ void update_gds_msr(void)
case GDS_MITIGATION_FORCE:
case GDS_MITIGATION_UCODE_NEEDED:
case GDS_MITIGATION_HYPERVISOR:
+ case GDS_MITIGATION_AUTO:
return;
}

@@ -883,13 +887,16 @@ static void __init gds_select_mitigation(void)

if (boot_cpu_has(X86_FEATURE_HYPERVISOR)) {
gds_mitigation = GDS_MITIGATION_HYPERVISOR;
- goto out;
+ return;
}

if (cpu_mitigations_off())
gds_mitigation = GDS_MITIGATION_OFF;
/* Will verify below that mitigation _can_ be disabled */

+ if (gds_mitigation == GDS_MITIGATION_AUTO)
+ gds_mitigation = GDS_MITIGATION_FULL;
+
/* No microcode */
if (!(x86_arch_cap_msr & ARCH_CAP_GDS_CTRL)) {
if (gds_mitigation == GDS_MITIGATION_FORCE) {
@@ -902,7 +909,7 @@ static void __init gds_select_mitigation(void)
} else {
gds_mitigation = GDS_MITIGATION_UCODE_NEEDED;
}
- goto out;
+ return;
}

/* Microcode has mitigation, use it */
@@ -923,9 +930,16 @@ static void __init gds_select_mitigation(void)
*/
gds_mitigation = GDS_MITIGATION_FULL_LOCKED;
}
+}
+
+static void __init gds_apply_mitigation(void)
+{
+ if (!boot_cpu_has_bug(X86_BUG_GDS))
+ return;
+
+ if (x86_arch_cap_msr & ARCH_CAP_GDS_CTRL)
+ update_gds_msr();

- update_gds_msr();
-out:
pr_info("%s\n", gds_strings[gds_mitigation]);
}

--
2.34.1